What is the best way to feed our microbes? In one word: fiber. We have long known that fiber is good for us. It helps reduce caloric intake and maintain regularity. But it is also perhaps the most powerful tool we have to help our native microbes. It is their bread and butter, so to speak.
Fiber is made up of long chains of carbohydrates. Because these carbohydrates are connected by complicated bonds, these molecules are difficult — and sometimes impossible — for us to digest. We humans simply don’t have the enzymes necessary to break down many types of fiber. And that means these compounds end up, intact, down in the lower intestine, where helpful microbes can feast on these cast-offs. When these compounds encourage the growth and health of beneficial microbes, they are known as prebiotic.
In recent years and decades, we haven’t been very good at providing this expected fodder to our native microbes. And without fiber to nourish them, their populations take a dive, leaving us without their many benefits.
The average American now consumes about 15 grams of fiber per day, roughly half of what the U.S. government recommends. Those 30 or so recommended grams of fiber are likely about a third (or less) of what a more traditional diet might offer. Even the high end of this range is a fraction of what our ancestors probably ate every day. All of that means we’re eating just 10 to 15 percent of what our microbes would have expected. And they seem to be feeling the deficiency — as are we.
For example, one archaeological study of cave sites in the Chihuahuan Desert inhabited by humans for some 10,000 years found evidence of “intensive utilization” of local plants high in prebiotic fibers. Clues gathered from cooking materials, human skeletons, and coprolites (fossilized excrement) suggest that the inhabitants were eating some 135 grams of a specific type of microbe-feeding fiber (inulin) each day. The ancient desert dwellers might have been an exceptional case, but we know that through history, as a rule, humans had much more fibrous meals. Study after study points to the diversity of Paleolithic diets. An investigation of a 23,000-year-old site in Israel uncovered that the local cuisine included more than 142 different species of plants (including seeds, nuts, fruits, and cereals). Although the work didn’t specifically investigate the fiber content of the residents’ diet, the impressive diversity of plants at the site suggests meals rich in fiber — and many different forms of it at that.
When we do eat food that contains prebiotic fibers, gut microbes in turn repay us by making compounds that can help quell inflammation or defend us against infection. These compounds, known as metabolites, are microbial byproducts, expelled during microbes’ metabolic process of digesting food that comes their way. Fortunately, these byproducts just happen to be beneficial for us.
Beyond these health links, early studies in animals show another reason to feed microbes the foods they need: protection from food allergies. Our large intestine has just a thin barrier separating its contents from the rest of our bodies. When our resident microbes go hungry for too long, they start to eat through the better part of that barrier, opening up holes for all kinds of material to escape into the bloodstream, a condition known, unappealingly, as leaky gut. The body will spot this material as foreign and send the immune system into attack mode. This is certainly good if the escaped material is a harmful microbe, but if it is, say, a food particle, it could trigger or exacerbate food allergies.
Adding in more prebiotic food also means, simply, more helpful microbes. Some research has suggested that for every 10 grams of prebiotic carbohydrates that reach the gut microbiota, about three grams of additional bacteria blossom into life. That’s roughly 3 trillion new organisms for just adding those 10 grams of microbe fodder each day. Not a bad tradeoff for eating some extra whole grains — and cold potato salad.
So, when it comes to prebiotics, instead of “build it and they will come,” think “eat it and they will multiply” — and possibly even help protect you from a myriad of increasingly common health concerns. All it takes is paying a little more attention to what you’re feeding your microbes.